Water Velocity Sensor

This instructable describes how you can build your own water velocity sensor. The basis of this sensor is formed by a Photon and a potentiometer. An Arduino or Raspberry Pi will also do, but then you will have to write your own code. The rest of the sensor is built using scrap material. If you are going to build this it may look differently, but this instructable only describes how you can build it. If you want to make it with wood go ahead and use wood. Want to make it transparent? Go ahead and make it out of perspex.

What you'll need for this project:

• Particle Photon/ Arduino/ Raspberry Pi/ Other Dev Board
• Potentiometer
• Wires
• Breadboard (handy, but not compulsory)
• Pipe clamps
• Rods of any material
• Plates of any material
• Duct Tape (basis of every project)
• Screws, nuts, bolts
• Glue
• Tools

The frame is made out of two pieces from an old desk. For a clear view of the layout, we've made a 3D model that you can look at to get a basic view of the sensor. In this model the blue part is what we call the frame. The top part of the frame is to support the construction so you can suspend it anywhere you want. Bolted to the top part is the downward facing part. This is what provides the height so you can get the sensor into the water without getting the equipment wet. The height of this part is dependent on how deep your water level is relative to where you can suspend the frame. For easy adjustments we made two slits into the steel plate. In this way we can easily raise and lower the sensor. If the slits do not provide enough adjustment you can also drill new holes from where you can bolt the plate to the top part.

The paddle is the part that is in contact with the water. This is the part that can move and converts the kinetic energy of the water into something we can measure. In the 3D model the paddle is colored red. The paddle consists of a large plate, a vertical rod and a horizontal rod. The plate is the part that goes into the water, this is then connected to the vertical rod, which in its turn is then connected to the horizontal rod. The horizontal rod is connected to the steel plate using two pipe clamps, which were mounted into the slits. Be sure to not tighten the clamps too much since the paddle must still be able to rotate.

The wiring scheme for the sensor is quite simple You only have to connect the potentiometer (potmeter) to your development board. The two outer pins of the potmeter are connected to either the ground or the +3.3 volts (5V on Arduino), but make sure when the paddle is in the down position that the potentiometer has the highest resistance. The middle pin is the measurement pin this one is connected to one of the analog input pins labelled A0 to A5. The potmeter is then connected to the end of the horizontal rod of the paddle. Make sure to fasten it in such a way that the potmeter can not rotate when the paddle rotates. Otherwise you can't guarantee a reliable outcome of your sensor.

The code used for this sensor can be copied one to one to your Particle Photon, if you are using an Arduino most of the code can be reused (the online features won't work). There are some parameters that you will have to change. If you are going to upload the data to Thingspeak, then first make a Thingspeak account and create a channel. When you created a channel copy the API key and the channel number to the places defined in the code. We calibrated our sensor in a flow flume where we can simulate different flow scenarios, if you have this available you can calibrate your own sensor by placing floaters in the water and measuring their velocity. This can then be correlated to the measurements taken by the sensor. If you don't have access to such equipment you can use the formula that we created for our sensor. Your measurements might deviate from the real world velocity but at least you can say something about relative water speed.